SIEMENS
10/160
Siemens IC 10 · 2017
Relays
SIRIUS 3RN2 thermistor motor protection
10
.
CAUTION!
When used in a hazardous area, the thermistor motor protection
relay must not be operated with automatic RESET (terminal Y1
and Y2 permanently jumpered).
A risk analysis must be performed for the complete plant or
machine. If this analysis yields a lower hazard potential
(category 1), all SIRIUS 3RN2 thermistor motor protection relays
can be used, provided the safety regulations are observed.
.
WARNING!
All work involved in connecting, commissioning and mainte-
nance must be carried out by qualified, responsible personnel.
Improper handling may result in serious personal injury and
considerable damage to property.
Cable routing
The measuring circuit leads must be routed as separate control
cables. It is not permitted to use cores from the supply line of the
motor or any other main supply cables. If extreme inductive or
capacitive interference is expected as a result of power lines
routed in parallel, shielded control cables must be used.
Maximum length of sensor circuit cables for evaluation units
without short-circuit detection in the sensor circuit:
Maximum length of sensor circuit cables for evaluation units with
short-circuit detection
1)
1)
A short circuit in the sensor circuit will be detected up to this maximum
cable length.
Principle of operation
SIRIUS 3RN2 thermistor motor protection relays are thermal
protection devices that are suitable, in combination with type A
PTC thermistors, for monitoring temperatures of electrical drives,
transformer windings, oils, bearings, air, etc.
The most frequent application is monitoring of three-phase
motors in which the motor manufacturer has fitted a PTC sensor
into every winding overhang and in which these PTC sensors are
connected in series.
The SIRIUS 3RN2 thermistor motor protection relays operate
in accordance with the closed-circuit principle and therefore
monitor themselves for loss of supply voltage. The exceptions
are the warning output on 3RN2023, which always works on the
open-circuit principle and the bistable relays of the
3RN2012-.BW31, which always retain the last switching state.
A micro-interruption in the power supply of less than 30 ms does
not change the status of the output relays.
For devices with the "Manual RESET" function, the test function
can be activated and a trip simulated by pressing the blue
Test/RESET button for > 2 seconds.
The 3RN2011, 3RN2012, 3RN2013 and 3RN2023 devices are
additionally equipped with open-circuit and short-circuit detec-
tion in the sensor circuit. The unit will trip in the event of a short-
circuit (resistance in sensor circuit < 10
) or open circuit in the
sensor circuit (dynamic open-circuit detection). Tripping as the
result of a short-circuit in the sensor circuit is indicated by a flick-
ering red LED (TRIPPED). In the event of short-circuit in the sen-
sor circuit for warning on the 3RN2023, the yellow warning LED
flickers (WARNING)). The devices with dynamic open-circuit
detection evaluate the rise time of the sensor circuit resistance.
If the sensor circuit resistance rises from 3300
to 12 k
within
200 ms, the unit will not only trip, but also indicate the open
circuit via a flashing red LED (TRIPPED). In the event of an open
circuit in a sensor circuit, the yellow warning LED (WARNING)
flashes for the 3RN2023.
All evaluation units (except for the 3RN2000 compact evaluation
unit) feature electrical separation between the control circuit and
the sensor circuit. The relay outputs are also electrically sepa-
rated from all other circuits. The 3RN2013 and 3RN2023 evalua-
tion units incorporate protective electrical isolation between all
circuits up to
U
i
= 300 V.
3RN2000 compact evaluation unit
The compact unit, which is only 17.5 mm wide, is equipped with
a red LED (TRIPPED) for the tripped indicator and a changeover
contact. After the unit has tripped, it is automatically reset once
the thermistors have cooled down. The root of the changeover
contact is connected to the control voltage (terminal 11 is con-
nected to terminal A1). This unit is particularly suitable in circuits
in which the control circuit and signaling circuit have the same
potential, e.g. in local control boxes.
3RN2010, 3RN2011, 3RN2012,
and 3RN2013 compact/standard evaluation units
The units are equipped with two LEDs (READY and TRIPPED) for
an operating and tripped display and are available with either
1 NO + 1 NC contacts (3RN2010, overall width 17.5 mm) or with
2 CO contacts. Depending on the version, they are available
with Auto RESET (3RN2010), Manual/Remote RESET (3RN2011)
or Manual/Auto and Remote RESET (3RN2012 and 3RN2013).
Remote RESET can be achieved by connecting an external
pushbutton with a normally-open function to terminals Y1 and
Y2. If terminals Y1 and Y2 are jumpered, the unit is automatically
reset once the thermistors have cooled down (Auto RESET).
3RN2012 and 3RN2013 are non-volatile. This means a previous
trip remains stored in the event of a control supply voltage failure
- the thermistor motor protection relay remains in the safe state
with an opened output relay until it is intentionally reset by press-
ing the TEST/RESET button of the unit or an external pushbutton.
3RN2023 "Warning and disconnection"
Two sensor circuits can be connected to one 3RN2023 evalua-
tion unit that act on two separate output relays with 1 NO contact
for warning and 1 CO contact for disconnection. Thermistors
with different rated response temperatures TNF are used to im-
plement the "Warning" and "Disconnection" functions. When sen-
sor circuit 2 for "Warning" responds, a yellow LED is lit and when
the "Disconnection" circuit responds, a red LED is lit. The sensor
circuits have a different reset response and operating behavior:
the "Warning" thermistor sensor circuit 2 (terminals 2T1, T2)
works only with Auto RESET and according to the open-circuit
principle (output relay K2, NO contact). The "Disconnection"
thermistor sensor circuit 1, (terminals 1T1, T2) can be changed
from Manual RESET to Auto RESET by jumpering terminals Y1
and Y2. Remote RESET is implemented by connecting an exter-
nal pushbutton with a normally-open function to these terminals.
Cable cross-section
3RN2000, 3RN2010
2.5 mm²
2 x 2800 m
1.5 mm²
2 x 1500 m
0.5 mm²
2 x 500 m
Cable cross-section
3RN2011, 3RN2012, 3RN2013, 3RN2023
2.5 mm²
2 x 250 m
1.5 mm²
2 x 150 m
0.5 mm²
2 x 50 m
© Siemens AG 2016